Conventionally, a remote controller for unlocking and locking a door of a vehicle without operating a key of the vehicle is well known in, for example, JP-A-2000-104429. The remote controller transmits a request signal to a portable device, and receives a response signal from the portable device in accordance with the request signal so that the remote controller verifies the portable device based on the response signal. When the remote controller determines that the portable device is a proper key of the vehicle, and a door of the vehicle is locked, the remote controller unlocks the door.
In an in-vehicle device controller for transmitting a request signal to the portable device, receiving the response signal from the portable device in accordance with the request signal, and checking the portable device based on the response signal, a precondition should be satisfied for checking the portable device such that an user with the portable device is disposed in a detection area of the in-vehicle device controller on a vehicle side.
However, in a conventional in-vehicle device controller, a transmitting frequency of the response signal from the portable device is fixed. If the response signal is copied, the in-vehicle device controller may determine that the portable device is proper even when the user with the portable device is not disposed in the detection area of the in-vehicle device controller on the vehicle side.
Thus, it is considered that the portable device switches and transmits the response signal having different frequencies in response to the request signal in order to prevent a copy of the response signal.
However, when a switching pattern of the frequencies of the response signal is fixed, the third person may easily specify the switching pattern. When the third person specifies the switching pattern, the third person can copy the response signal by tuning a reception frequency according to the switching pattern. Thus, security of the remote controller is reduced.
Further, it is considered that the security of the remote controller is improved by increasing the number of transmitting times of the response signal with switching the frequency of the response signal. As the transmitting times of the response signal increases, a checking time for checking the response signal becomes longer. Thus, responsiveness of the remote controller is reduced.